The present invention relates to a service integrated digital transmission system of the type employing conducted light radiation transmission.
German Offenlegungsschrift [Laid-open Application] No. 2,538,638 discloses an integrated communications system for the transmission and switching of video, audio and data signals, wherein the subscriber terminal is connected to the associated central exchange by means of two separate glass fibers, one fiber being used for transmission and the other for reception of telephone and video signals in time multiplex. Optionally, video coupling fields are provided for video communications or for switching in television signals.
U.S. Application Ser. No. 155,132, filed May 30, 1980, discloses a service integrated communications transmission and switching system for audio, video and data signals in which only one light conductive fiber is used for the subscriber terminal line and wherein narrowband service is provided by digital transmission and multiplexing at the subscriber end, and broadband service is provided by means of an analog transmission. In this system, the wave multiplex method is proposed for two-way transmissions which, however, places high demands on the optical transmission and receiving elements as well as the couplers with respect to cross-talk attenuation.
European Patent Application EP No. 0 012 979 A1 discloses a method for transmitting a plurality of signals over one lightwave conductor connection, particularly between a central office and a subcriber terminal, wherein television signals, a video telephone signal, monaural and stereo audio signals and a digital telephone signal are pulse position modulated and combined into a time multiplex signal. It is proposed to build a frame for the time multiplex signal to be transmitted in dependence on the simplest possible multiplexer and demultiplexer structure as well as a frame wherein a pulse of the lower channel is given a comparatively longer time rise. It is further proposed to combine the audio signals into a frequency multiplex signal and to likewise reshape this signal into a pulse position modulated signal.